FIG. 1A illustrates a typical device for actuating a valve, damper or the like. An electric motor 10 is coupled to a drive shaft 12 by gears 14, 16. Also coupled to a drive shaft is a mechanical end stop including a stopper 18 disposed relative to an attachment 20 that is secured via disk 22 to the drive shaft 12. As shown by FIGS. 1B-1C, as the drive shaft 12 rotates, the disk 22 causes the attachment 20 to eventually bump against the stopper 18, preventing further motion. For at least a brief time, the electric motor 10 may continue driving the drive shaft against the mechanical end stop provided by the stopper 18 and attachment 20. A second stopper may also be provided to further limit motion in another direction. Various supporting elements, which would hold the drive shaft 12, stopper 18, attachment 20 and disk 22, among other elements, in alignment, are omitted in the figures for simplicity.
Various alternatives to this arrangement are known, for example, allowing the part being actuated (a valve, damper, or the like) to provide a physical end stop (for example, when the damper is closed and cannot move farther) for the actuator. Another is to provide a switch relative to the drive shaft that is actuated when the drive shaft reaches a desired position. Each of these solutions presents various difficulties, including complexity of installation, expense of additional parts, and (especially with some physical barrier-type end stops) fatigue and stress on parts that cause the end stop, as well as strain on the electric motor 10, drive shaft 12 and gears 14, 16. Better solutions are desired.